Analysis of tin, lead or tin-lead alloy plating solution

Abstract

In electroless or electric tin, lead or tin-lead alloy plating solution which may contain copper, the concentration of a metal ion component selected from divalent tin ion, lead ion, and copper ion is quantitatively determined by taking a sample from the solution, adding a chemical agent, for example, an oxidizing agent to the sample, thereby causing the selected metal ion to develop its color, measuring the absorbance of the sample due to the metal ion by colorimetry, and determining the concentration from the absorbance. A choice of chemical agent depends on a particular metal ion on analysis. When the solution contains more than one metal ion, correction is made by repeating the process using another chemical agent.

We claim: 
     
       1. A method for analyzing a tin, lead or tin-lead alloy plating solution having copper dissolved therein as a complex with thiourea or its derivative in the plating solution comprising the steps of: taking a sample from the solution,   adding an oxidizing agent to said sample, thereby simultaneously decomposing thiourea or its derivative and oxidizing a monovalent copper ion in the sample to a divalent copper ion,   adjusting the pH of said sample to between pH 4 and pH 11,   adding a color developing agent to said sample, thereby causing the divalent copper ion to develop its color, and   quantitatively determining the concentration of divalent copper ion by colorimetry.   
     
     
       2. The method of claim 1 wherein said color developing agent is selected from the group consisting of ammonia, amines, 2,2'-bipyridyl, 1,10-phenanthroline and phenanthroline derivatives. 
     
     
       3. A method for analyzing a tin, lead or tin-lead alloy plating solution containing at least one divalent metal ion selected from the group consisting of tin and lead ions, comprising the steps of: taking a sample from the solution,   adding thiourea or its derivative to the sample thereby causing the divalent metal ion to develop its color, and   quantitatively determining the concentration of the divalent metal ion by colorimetry.   
     
     
       4. A method for analyzing a lead or tin-lead alloy plating solution containing a copper ion in addition to a lead ion, comprising the steps of: taking a sample from the solution,   adding an oxidizing agent to said sample thereby simultaneously decomposing thiourea or its derivative and oxidizing a monovalent copper ion in the sample to a divalent copper ion,   adjusting the pH of said sample to between pH 4 and pH 11,   adding a color developing agent to said sample thereby causing the divalent copper ion to develop its color, and   quantitatively determining the concentration of divalent copper ion by colorimetry   taking a second sample from the solution,   adding an iodine to said second sample, causing said lead and copper ions to develop their color,   quantitatively determining the combined concentration of said lead and copper ions by colorimetry, and   subtracting said concentration of copper ion from said combined concentration to provide a quantitative determination of lead ion.   
     
     
       5. A method for analyzing a tin-lead alloy plating solution for quantitative determination of divalent tin ion and lead ion, comprising the steps of: taking a first sample from the solution,   adding an iodide as a color developing agent to said first sample thereby causing said lead ion to develop its color,   quantitatively determining the concentration of said lead ion by colorimetry,   taking a second sample from the solution,   adding thiourea or its derivative to said second sample thereby causing said divalent tin ion and lead ion to develop their color,   quantitatively determining the combined concentration of said divalent tin and lead ions by colorimetry, and   subtracting said concentration of lead ion from said combined concentration of divalent tin and lead ions to provide the concentration of divalent tin ion.   
     
     
       6. A method for analyzing a tin-lead alloy plating solution containing copper ion for quantitative determination of divalent tin ion and lead ion, the method comprising the steps of: determining the copper ion concentration of the solution,   taking a first sample from the solution,   adding an iodide to said first sample thereby causing said lead ion and copper ion to develop their color,   quantitatively determining the combined concentration of lead and copper ions by colorimetry,   subtracting said concentration of copper ion from said combined concentration of lead and copper ions to provide a quantitative determination of lead ion,   taking a second sample from the solution,   adding thiourea or its derivative to said second sample thereby causing said divalent tin ion and lead ion to develop their color,   quantitatively determining the combined concentration of said divalent tin and lead ions by colorimetry, and   subtracting said concentration of lead ion from said combined concentration of divalent tin and lead ions to provide a quantitative determination of divalent tin ion.   
     
     
       7. A method for analyzing an electroless tin-lead alloy plating solution for quantitative determination of copper ion, lead ion, and divalent tin ion, comprising the steps of: Step 1: taking a first sample from the solution, adding an oxidizing agent to said first sample, thereby converting a monovalent copper ion to a divalent copper ion, and determining the concentration of copper ion by colorimetry,   Step 2: taking a second sample from the solution, adding an iodide to said second sample, measuring the absorbance of said second sample to provide a combined absorbance of copper and lead ions, subtracting an absorbance attributable to copper ion as calculated from the concentration of copper ion determined in Step 1 from the combined absorbance to provide an absorbance attributable to only lead ion, and calculating the concentration of lead ion from the absorbance of lead ion, and   Step 3: taking a third sample from the solution, adding thiourea or its derivative to said third sample, measuring the absorbance of said third sample to provide a combined absorbance of divalent tin and lead ions, subtracting an absorbance attributable to lead ion s calculated from the concentration of lead ion determined in Step 2 from the combined absorbance to provide an absorbance attributable to only divalent tin ion, and calculating the concentration of divalent tin ion from the absorbance of divalent tin ion.   
     
     
       8. The method of claim 1 further comprising the step of adding a complexing agent capable of forming complexes with Tin (IV) and Lead (II), prior to the colorimetric determination. 
     
     
       9. The method of claim 8, wherein said complexing agent is selected from the group consisting of oxalic acid, tartaric acid, citric acid, EDTA and its salts, and triethanol amine. 
     
     
       10. The method of claim 1, wherein said oxidizing agent is selected from the group consisting of peroxides, persulfates, chlorous acid and chlorites. 
     
     
       11. The method of claim 10, wherein said oxidizing agent is hydrogen peroxide. 
     
     
       12. The method of claim 1, wherein said quantitative colorimetric determination of the concentration of divalent copper ion is performed in the range of wavelengths from 500 to 800 nm. 
     
     
       13. The method of claim 3, wherein said thiourea derivative is selected from the group consisting of dimethylthiourea, diethylthiourea, dimethylolthiourea and diphenylthiourea. 
     
     
       14. The method of claim 3, further comprising the step of adding a reducing agent for converting tetravalent tin ions into divalent tin ions, prior to the addition of thiourea. 
     
     
       15. The method of claim 14 wherein said reducing agent is selected from the group consisting of metallic zinc powder, tetrahydroborates, hydrazine and hydrazine salts. 
     
     
       16. The method of claim 4, wherein said iodide is selected from the group consisting of potassium iodide and sodium iodide. 
     
     
       17. The method of claim 5, wherein said iodide is selected from the group consisting of potassium iodide and sodium iodide. 
     
     
       18. The method of claim 6, wherein said iodide is selected from the group consisting of potassium iodide and sodium iodide. 
     
     
       19. The method of claim 7, wherein said iodide is selected from the group consisting of potassium iodide and sodium iodide. 
     
     
       20. The method of claim 5, wherein said thiourea derivative is selected from the group consisting of dimethylthiourea, diethylthiourea, dimethylolthiourea and diphenylthiourea. 
     
     
       21. The method of claim 6, wherein said thiourea derivative is selected from the group consisting of dimethylthiourea, diethylthiourea, dimethylolthiourea and diphenylthiourea. 
     
     
       22. The method of claim 7, wherein said oxidizing agent is selected from the group consisting of peroxides, persulfates, chlorous acid and chlorites. 
     
     
       23. The method of claim 4, further comprising the step of adding a complexing agent selected from the group consisting of oxalic acid, tartaric acid, citric acid, EDTA, hydroxyphosphoric acid and salts thereof. 
     
     
       24. The method of claim 6, further comprising the step of adding a complexing agent selected from the group consisting of oxalic acid, tartaric acid, citric acid, EDTA, hydroxyphosphoric acid and salts thereof. 
     
     
       25. The method of claim 7, further comprising the step of adding a complexing agent selected from the group consisting of oxalic acid, tartaric acid, citric acid, EDTA, hydroxyphosphoric acid and salts thereof.